FFmpeg/libavcodec/h264_refs.c

/*
 * H.26L/H.264/AVC/JVT/14496-10/... reference picture handling
 * Copyright (c) 2003 Michael Niedermayer <michaelni@gmx.at>
 *
 * This file is part of Libav.
 *
 * Libav is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * Libav is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with Libav; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file
 * H.264 / AVC / MPEG-4 part10  reference picture handling.
 * @author Michael Niedermayer <michaelni@gmx.at>
 */

#include <inttypes.h>

#include "internal.h"
#include "avcodec.h"
#include "h264.h"
#include "golomb.h"
#include "mpegutils.h"

#include <assert.h>

static void pic_as_field(H264Ref *pic, const int parity)
{
    int i;
    for (i = 0; i < FF_ARRAY_ELEMS(pic->data); ++i) {
        if (parity == PICT_BOTTOM_FIELD)
            pic->data[i]   += pic->linesize[i];
        pic->reference      = parity;
        pic->linesize[i] *= 2;
    }
    pic->poc = pic->parent->field_poc[parity == PICT_BOTTOM_FIELD];
}

static void ref_from_h264pic(H264Ref *dst, H264Picture *src)
{
    memcpy(dst->data,     src->f->data,     sizeof(dst->data));
    memcpy(dst->linesize, src->f->linesize, sizeof(dst->linesize));
    dst->reference = src->reference;
    dst->poc       = src->poc;
    dst->pic_id    = src->pic_id;
    dst->parent = src;
}

static int split_field_copy(H264Ref *dest, H264Picture *src, int parity, int id_add)
{
    int match = !!(src->reference & parity);

    if (match) {
        ref_from_h264pic(dest, src);
        if (parity != PICT_FRAME) {
            pic_as_field(dest, parity);
            dest->pic_id *= 2;
            dest->pic_id += id_add;
        }
    }

    return match;
}

static int build_def_list(H264Ref *def, int def_len,
                          H264Picture * const *in, int len, int is_long, int sel)
{
    int  i[2] = { 0 };
    int index = 0;

    while ((i[0] < len || i[1] < len) && index < def_len) {
        while (i[0] < len && !(in[i[0]] && (in[i[0]]->reference & sel)))
            i[0]++;
        while (i[1] < len && !(in[i[1]] && (in[i[1]]->reference & (sel ^ 3))))
            i[1]++;
        if (i[0] < len && index < def_len) {
            in[i[0]]->pic_id = is_long ? i[0] : in[i[0]]->frame_num;
            split_field_copy(&def[index++], in[i[0]++], sel, 1);
        }
        if (i[1] < len && index < def_len) {
            in[i[1]]->pic_id = is_long ? i[1] : in[i[1]]->frame_num;
            split_field_copy(&def[index++], in[i[1]++], sel ^ 3, 0);
        }
    }

    return index;
}

static int add_sorted(H264Picture **sorted, H264Picture * const *src,
                      int len, int limit, int dir)
{
    int i, best_poc;
    int out_i = 0;

    for (;;) {
        best_poc = dir ? INT_MIN : INT_MAX;

        for (i = 0; i < len; i++) {
            const int poc = src[i]->poc;
            if (((poc > limit) ^ dir) && ((poc < best_poc) ^ dir)) {
                best_poc      = poc;
                sorted[out_i] = src[i];
            }
        }
        if (best_poc == (dir ? INT_MIN : INT_MAX))
            break;
        limit = sorted[out_i++]->poc - dir;
    }
    return out_i;
}

static void h264_initialise_ref_list(const H264Context *h, H264SliceContext *sl)
{
    int i, len;

    if (sl->slice_type_nos == AV_PICTURE_TYPE_B) {
        H264Picture *sorted[32];
        int cur_poc, list;
        int lens[2];

        if (FIELD_PICTURE(h))
            cur_poc = h->cur_pic_ptr->field_poc[h->picture_structure == PICT_BOTTOM_FIELD];
        else
            cur_poc = h->cur_pic_ptr->poc;

        for (list = 0; list < 2; list++) {
            len  = add_sorted(sorted,       h->short_ref, h->short_ref_count, cur_poc, 1 ^ list);
            len += add_sorted(sorted + len, h->short_ref, h->short_ref_count, cur_poc, 0 ^ list);
            assert(len <= 32);

            len  = build_def_list(sl->ref_list[list], FF_ARRAY_ELEMS(sl->ref_list[0]),
                                  sorted, len, 0, h->picture_structure);
            len += build_def_list(sl->ref_list[list] + len,
                                  FF_ARRAY_ELEMS(sl->ref_list[0]) - len,
                                  h->long_ref, 16, 1, h->picture_structure);

            if (len < sl->ref_count[list])
                memset(&sl->ref_list[list][len], 0, sizeof(H264Ref) * (sl->ref_count[list] - len));
            lens[list] = len;
        }

        if (lens[0] == lens[1] && lens[1] > 1) {
            for (i = 0; i < lens[0] &&
                        sl->ref_list[0][i].parent->f->buf[0]->buffer ==
                        sl->ref_list[1][i].parent->f->buf[0]->buffer; i++);
            if (i == lens[0]) {
                FFSWAP(H264Ref, sl->ref_list[1][0], sl->ref_list[1][1]);
            }
        }
    } else {
        len  = build_def_list(sl->ref_list[0], FF_ARRAY_ELEMS(sl->ref_list[0]),
                              h->short_ref, h->short_ref_count, 0, h->picture_structure);
        len += build_def_list(sl->ref_list[0] + len,
                              FF_ARRAY_ELEMS(sl->ref_list[0]) - len,
                              h-> long_ref, 16, 1, h->picture_structure);

        if (len < sl->ref_count[0])
            memset(&sl->ref_list[0][len], 0, sizeof(H264Ref) * (sl->ref_count[0] - len));
    }
}

/**
 * print short term list
 */
static void print_short_term(const H264Context *h)
{
    uint32_t i;
    if (h->avctx->debug & FF_DEBUG_MMCO) {
        av_log(h->avctx, AV_LOG_DEBUG, "short term list:\n");
        for (i = 0; i < h->short_ref_count; i++) {
            H264Picture *pic = h->short_ref[i];
            av_log(h->avctx, AV_LOG_DEBUG, "%"PRIu32" fn:%d poc:%d %p\n",
                   i, pic->frame_num, pic->poc, pic->f->data[0]);
        }
    }
}

/**
 * print long term list
 */
static void print_long_term(const H264Context *h)
{
    uint32_t i;
    if (h->avctx->debug & FF_DEBUG_MMCO) {
        av_log(h->avctx, AV_LOG_DEBUG, "long term list:\n");
        for (i = 0; i < 16; i++) {
            H264Picture *pic = h->long_ref[i];
            if (pic) {
                av_log(h->avctx, AV_LOG_DEBUG, "%"PRIu32" fn:%d poc:%d %p\n",
                       i, pic->frame_num, pic->poc, pic->f->data[0]);
            }
        }
    }
}

/**
 * Extract structure information about the picture described by pic_num in
 * the current decoding context (frame or field). Note that pic_num is
 * picture number without wrapping (so, 0<=pic_num<max_pic_num).
 * @param pic_num picture number for which to extract structure information
 * @param structure one of PICT_XXX describing structure of picture
 *                      with pic_num
 * @return frame number (short term) or long term index of picture
 *         described by pic_num
 */
static int pic_num_extract(const H264Context *h, int pic_num, int *structure)
{
    *structure = h->picture_structure;
    if (FIELD_PICTURE(h)) {
        if (!(pic_num & 1))
            /* opposite field */
            *structure ^= PICT_FRAME;
        pic_num >>= 1;
    }

    return pic_num;
}

static void h264_fill_mbaff_ref_list(H264SliceContext *sl)
{
    int list, i, j;
    for (list = 0; list < sl->list_count; list++) {
        for (i = 0; i < sl->ref_count[list]; i++) {
            H264Ref *frame = &sl->ref_list[list][i];
            H264Ref *field = &sl->ref_list[list][16 + 2 * i];

            field[0] = *frame;

            for (j = 0; j < 3; j++)
                field[0].linesize[j] <<= 1;
            field[0].reference = PICT_TOP_FIELD;
            field[0].poc       = field[0].parent->field_poc[0];

            field[1] = field[0];

            for (j = 0; j < 3; j++)
                field[1].data[j] += frame->parent->f->linesize[j];
            field[1].reference = PICT_BOTTOM_FIELD;
            field[1].poc       = field[1].parent->field_poc[1];
        }
    }
}

int ff_h264_decode_ref_pic_list_reordering(const H264Context *h, H264SliceContext *sl)
{
    int list, index, pic_structure;

    print_short_term(h);
    print_long_term(h);

    h264_initialise_ref_list(h, sl);

    for (list = 0; list < sl->list_count; list++) {
        if (get_bits1(&sl->gb)) {    // ref_pic_list_modification_flag_l[01]
            int pred = h->curr_pic_num;

            for (index = 0; ; index++) {
                unsigned int modification_of_pic_nums_idc = get_ue_golomb_31(&sl->gb);
                unsigned int pic_id;
                int i;
                H264Picture *ref = NULL;

                if (modification_of_pic_nums_idc == 3)
                    break;

                if (index >= sl->ref_count[list]) {
                    av_log(h->avctx, AV_LOG_ERROR, "reference count overflow\n");
                    return -1;
                }

                switch (modification_of_pic_nums_idc) {
                case 0:
                case 1: {
                    const unsigned int abs_diff_pic_num = get_ue_golomb(&sl->gb) + 1;
                    int frame_num;

                    if (abs_diff_pic_num > h->max_pic_num) {
                        av_log(h->avctx, AV_LOG_ERROR,
                               "abs_diff_pic_num overflow\n");
                        return AVERROR_INVALIDDATA;
                    }

                    if (modification_of_pic_nums_idc == 0)
                        pred -= abs_diff_pic_num;
                    else
                        pred += abs_diff_pic_num;
                    pred &= h->max_pic_num - 1;

                    frame_num = pic_num_extract(h, pred, &pic_structure);

                    for (i = h->short_ref_count - 1; i >= 0; i--) {
                        ref = h->short_ref[i];
                        assert(ref->reference);
                        assert(!ref->long_ref);
                        if (ref->frame_num == frame_num &&
                            (ref->reference & pic_structure))
                            break;
                    }
                    if (i >= 0)
                        ref->pic_id = pred;
                    break;
                }
                case 2: {
                    int long_idx;
                    pic_id = get_ue_golomb(&sl->gb); // long_term_pic_idx

                    long_idx = pic_num_extract(h, pic_id, &pic_structure);

                    if (long_idx > 31) {
                        av_log(h->avctx, AV_LOG_ERROR,
                               "long_term_pic_idx overflow\n");
                        return AVERROR_INVALIDDATA;
                    }
                    ref = h->long_ref[long_idx];
                    assert(!(ref && !ref->reference));
                    if (ref && (ref->reference & pic_structure)) {
                        ref->pic_id = pic_id;
                        assert(ref->long_ref);
                        i = 0;
                    } else {
                        i = -1;
                    }
                    break;
                }
                default:
                    av_log(h->avctx, AV_LOG_ERROR,
                           "illegal modification_of_pic_nums_idc %u\n",
                           modification_of_pic_nums_idc);
                    return AVERROR_INVALIDDATA;
                }

                if (i < 0) {
                    av_log(h->avctx, AV_LOG_ERROR,
                           "reference picture missing during reorder\n");
                    memset(&sl->ref_list[list][index], 0, sizeof(sl->ref_list[0][0])); // FIXME
                } else {
                    for (i = index; i + 1 < sl->ref_count[list]; i++) {
                        if (sl->ref_list[list][i].parent &&
                            ref->long_ref == sl->ref_list[list][i].parent->long_ref &&
                            ref->pic_id   == sl->ref_list[list][i].pic_id)
                            break;
                    }
                    for (; i > index; i--) {
                        sl->ref_list[list][i] = sl->ref_list[list][i - 1];
                    }
                    ref_from_h264pic(&sl->ref_list[list][index], ref);
                    if (FIELD_PICTURE(h)) {
                        pic_as_field(&sl->ref_list[list][index], pic_structure);
                    }
                }
            }
        }
    }
    for (list = 0; list < sl->list_count; list++) {
        for (index = 0; index < sl->ref_count[list]; index++) {
            if (!sl->ref_list[list][index].parent) {
                av_log(h->avctx, AV_LOG_ERROR, "Missing reference picture\n");
                if (index == 0 || h->avctx->err_recognition & AV_EF_EXPLODE)
                    return AVERROR_INVALIDDATA;
                else
                    sl->ref_list[list][index] = sl->ref_list[list][index - 1];
            }
        }
    }

    if (FRAME_MBAFF(h))
        h264_fill_mbaff_ref_list(sl);

    return 0;
}

/**
 * Mark a picture as no longer needed for reference. The refmask
 * argument allows unreferencing of individual fields or the whole frame.
 * If the picture becomes entirely unreferenced, but is being held for
 * display purposes, it is marked as such.
 * @param refmask mask of fields to unreference; the mask is bitwise
 *                anded with the reference marking of pic
 * @return non-zero if pic becomes entirely unreferenced (except possibly
 *         for display purposes) zero if one of the fields remains in
 *         reference
 */
static inline int unreference_pic(H264Context *h, H264Picture *pic, int refmask)
{
    int i;
    if (pic->reference &= refmask) {
        return 0;
    } else {
        for(i = 0; h->delayed_pic[i]; i++)
            if(pic == h->delayed_pic[i]){
                pic->reference = DELAYED_PIC_REF;
                break;
            }
        return 1;
    }
}

/**
 * Find a H264Picture in the short term reference list by frame number.
 * @param frame_num frame number to search for
 * @param idx the index into h->short_ref where returned picture is found
 *            undefined if no picture found.
 * @return pointer to the found picture, or NULL if no pic with the provided
 *                 frame number is found
 */
static H264Picture *find_short(H264Context *h, int frame_num, int *idx)
{
    int i;

    for (i = 0; i < h->short_ref_count; i++) {
        H264Picture *pic = h->short_ref[i];
        if (h->avctx->debug & FF_DEBUG_MMCO)
            av_log(h->avctx, AV_LOG_DEBUG, "%d %d %p\n", i, pic->frame_num, pic);
        if (pic->frame_num == frame_num) {
            *idx = i;
            return pic;
        }
    }
    return NULL;
}

/**
 * Remove a picture from the short term reference list by its index in
 * that list.  This does no checking on the provided index; it is assumed
 * to be valid. Other list entries are shifted down.
 * @param i index into h->short_ref of picture to remove.
 */
static void remove_short_at_index(H264Context *h, int i)
{
    assert(i >= 0 && i < h->short_ref_count);
    h->short_ref[i] = NULL;
    if (--h->short_ref_count)
        memmove(&h->short_ref[i], &h->short_ref[i + 1],
                (h->short_ref_count - i) * sizeof(H264Picture*));
}

/**
 * @return the removed picture or NULL if an error occurs
 */
static H264Picture *remove_short(H264Context *h, int frame_num, int ref_mask)
{
    H264Picture *pic;
    int i;

    if (h->avctx->debug & FF_DEBUG_MMCO)
        av_log(h->avctx, AV_LOG_DEBUG, "remove short %d count %d\n", frame_num, h->short_ref_count);

    pic = find_short(h, frame_num, &i);
    if (pic) {
        if (unreference_pic(h, pic, ref_mask))
            remove_short_at_index(h, i);
    }

    return pic;
}

/**
 * Remove a picture from the long term reference list by its index in
 * that list.
 * @return the removed picture or NULL if an error occurs
 */
static H264Picture *remove_long(H264Context *h, int i, int ref_mask)
{
    H264Picture *pic;

    pic = h->long_ref[i];
    if (pic) {
        if (unreference_pic(h, pic, ref_mask)) {
            assert(h->long_ref[i]->long_ref == 1);
            h->long_ref[i]->long_ref = 0;
            h->long_ref[i]           = NULL;
            h->long_ref_count--;
        }
    }

    return pic;
}

void ff_h264_remove_all_refs(H264Context *h)
{
    int i;

    for (i = 0; i < 16; i++) {
        remove_long(h, i, 0);
    }
    assert(h->long_ref_count == 0);

    for (i = 0; i < h->short_ref_count; i++) {
        unreference_pic(h, h->short_ref[i], 0);
        h->short_ref[i] = NULL;
    }
    h->short_ref_count = 0;
}

static int check_opcodes(MMCO *mmco1, MMCO *mmco2, int n_mmcos)
{
    int i;

    for (i = 0; i < n_mmcos; i++) {
        if (mmco1[i].opcode != mmco2[i].opcode)
            return -1;
    }

    return 0;
}

int ff_generate_sliding_window_mmcos(H264Context *h, int first_slice)
{
    MMCO mmco_temp[MAX_MMCO_COUNT], *mmco = first_slice ? h->mmco : mmco_temp;
    int mmco_index = 0, i = 0;

    assert(h->long_ref_count + h->short_ref_count <= h->ps.sps->ref_frame_count);

    if (h->short_ref_count &&
        h->long_ref_count + h->short_ref_count == h->ps.sps->ref_frame_count &&
        !(FIELD_PICTURE(h) && !h->first_field && h->cur_pic_ptr->reference)) {
        mmco[0].opcode        = MMCO_SHORT2UNUSED;
        mmco[0].short_pic_num = h->short_ref[h->short_ref_count - 1]->frame_num;
        mmco_index            = 1;
        if (FIELD_PICTURE(h)) {
            mmco[0].short_pic_num *= 2;
            mmco[1].opcode         = MMCO_SHORT2UNUSED;
            mmco[1].short_pic_num  = mmco[0].short_pic_num + 1;
            mmco_index             = 2;
        }
    }

    if (first_slice) {
        h->mmco_index = mmco_index;
    } else if (!first_slice && mmco_index >= 0 &&
               (mmco_index != h->mmco_index ||
                (i = check_opcodes(h->mmco, mmco_temp, mmco_index)))) {
        av_log(h->avctx, AV_LOG_ERROR,
               "Inconsistent MMCO state between slices [%d, %d, %d]\n",
               mmco_index, h->mmco_index, i);
        return AVERROR_INVALIDDATA;
    }
    return 0;
}

int ff_h264_execute_ref_pic_marking(H264Context *h, MMCO *mmco, int mmco_count)
{
    int i, av_uninit(j);
    int current_ref_assigned = 0, err = 0;
    H264Picture *av_uninit(pic);

    if ((h->avctx->debug & FF_DEBUG_MMCO) && mmco_count == 0)
        av_log(h->avctx, AV_LOG_DEBUG, "no mmco here\n");

    for (i = 0; i < mmco_count; i++) {
        int av_uninit(structure), av_uninit(frame_num);
        if (h->avctx->debug & FF_DEBUG_MMCO)
            av_log(h->avctx, AV_LOG_DEBUG, "mmco:%d %d %d\n", h->mmco[i].opcode,
                   h->mmco[i].short_pic_num, h->mmco[i].long_arg);

        if (mmco[i].opcode == MMCO_SHORT2UNUSED ||
            mmco[i].opcode == MMCO_SHORT2LONG) {
            frame_num = pic_num_extract(h, mmco[i].short_pic_num, &structure);
            pic       = find_short(h, frame_num, &j);
            if (!pic) {
                if (mmco[i].opcode != MMCO_SHORT2LONG ||
                    !h->long_ref[mmco[i].long_arg]    ||
                    h->long_ref[mmco[i].long_arg]->frame_num != frame_num) {
                    av_log(h->avctx, AV_LOG_ERROR, "mmco: unref short failure\n");
                    err = AVERROR_INVALIDDATA;
                }
                continue;
            }
        }

        switch (mmco[i].opcode) {
        case MMCO_SHORT2UNUSED:
            if (h->avctx->debug & FF_DEBUG_MMCO)
                av_log(h->avctx, AV_LOG_DEBUG, "mmco: unref short %d count %d\n",
                       h->mmco[i].short_pic_num, h->short_ref_count);
            remove_short(h, frame_num, structure ^ PICT_FRAME);
            break;
        case MMCO_SHORT2LONG:
                if (h->long_ref[mmco[i].long_arg] != pic)
                    remove_long(h, mmco[i].long_arg, 0);

                remove_short_at_index(h, j);
                h->long_ref[ mmco[i].long_arg ] = pic;
                if (h->long_ref[mmco[i].long_arg]) {
                    h->long_ref[mmco[i].long_arg]->long_ref = 1;
                    h->long_ref_count++;
                }
            break;
        case MMCO_LONG2UNUSED:
            j   = pic_num_extract(h, mmco[i].long_arg, &structure);
            pic = h->long_ref[j];
            if (pic) {
                remove_long(h, j, structure ^ PICT_FRAME);
            } else if (h->avctx->debug & FF_DEBUG_MMCO)
                av_log(h->avctx, AV_LOG_DEBUG, "mmco: unref long failure\n");
            break;
        case MMCO_LONG:
                    // Comment below left from previous code as it is an interesting note.
                    /* First field in pair is in short term list or
                     * at a different long term index.
                     * This is not allowed; see 7.4.3.3, notes 2 and 3.
                     * Report the problem and keep the pair where it is,
                     * and mark this field valid.
                     */
            if (h->short_ref[0] == h->cur_pic_ptr)
                remove_short_at_index(h, 0);

            /* make sure the current picture is not already assigned as a long ref */
            if (h->cur_pic_ptr->long_ref) {
                for (j = 0; j < FF_ARRAY_ELEMS(h->long_ref); j++) {
                    if (h->long_ref[j] == h->cur_pic_ptr)
                        remove_long(h, j, 0);
                }
            }


            if (h->long_ref[mmco[i].long_arg] != h->cur_pic_ptr) {
                remove_long(h, mmco[i].long_arg, 0);

                h->long_ref[mmco[i].long_arg]           = h->cur_pic_ptr;
                h->long_ref[mmco[i].long_arg]->long_ref = 1;
                h->long_ref_count++;
            }

            h->cur_pic_ptr->reference |= h->picture_structure;
            current_ref_assigned = 1;
            break;
        case MMCO_SET_MAX_LONG:
            assert(mmco[i].long_arg <= 16);
            // just remove the long term which index is greater than new max
            for (j = mmco[i].long_arg; j < 16; j++) {
                remove_long(h, j, 0);
            }
            break;
        case MMCO_RESET:
            while (h->short_ref_count) {
                remove_short(h, h->short_ref[0]->frame_num, 0);
            }
            for (j = 0; j < 16; j++) {
                remove_long(h, j, 0);
            }
            h->poc.frame_num = h->cur_pic_ptr->frame_num = 0;
            h->mmco_reset = 1;
            h->cur_pic_ptr->mmco_reset = 1;
            break;
        default: assert(0);
        }
    }

    if (!current_ref_assigned) {
        /* Second field of complementary field pair; the first field of
         * which is already referenced. If short referenced, it
         * should be first entry in short_ref. If not, it must exist
         * in long_ref; trying to put it on the short list here is an
         * error in the encoded bit stream (ref: 7.4.3.3, NOTE 2 and 3).
         */
        if (h->short_ref_count && h->short_ref[0] == h->cur_pic_ptr) {
            /* Just mark the second field valid */
            h->cur_pic_ptr->reference = PICT_FRAME;
        } else if (h->cur_pic_ptr->long_ref) {
            av_log(h->avctx, AV_LOG_ERROR, "illegal short term reference "
                                           "assignment for second field "
                                           "in complementary field pair "
                                           "(first field is long term)\n");
            err = AVERROR_INVALIDDATA;
        } else {
            pic = remove_short(h, h->cur_pic_ptr->frame_num, 0);
            if (pic) {
                av_log(h->avctx, AV_LOG_ERROR, "illegal short term buffer state detected\n");
                err = AVERROR_INVALIDDATA;
            }

            if (h->short_ref_count)
                memmove(&h->short_ref[1], &h->short_ref[0],
                        h->short_ref_count * sizeof(H264Picture*));

            h->short_ref[0] = h->cur_pic_ptr;
            h->short_ref_count++;
            h->cur_pic_ptr->reference |= h->picture_structure;
        }
    }

    if (h->long_ref_count + h->short_ref_count -
        (h->short_ref[0] == h->cur_pic_ptr) > h->ps.sps->ref_frame_count) {

        /* We have too many reference frames, probably due to corrupted
         * stream. Need to discard one frame. Prevents overrun of the
         * short_ref and long_ref buffers.
         */
        av_log(h->avctx, AV_LOG_ERROR,
               "number of reference frames (%d+%d) exceeds max (%d; probably "
               "corrupt input), discarding one\n",
               h->long_ref_count, h->short_ref_count, h->ps.sps->ref_frame_count);
        err = AVERROR_INVALIDDATA;

        if (h->long_ref_count && !h->short_ref_count) {
            for (i = 0; i < 16; ++i)
                if (h->long_ref[i])
                    break;

            assert(i < 16);
            remove_long(h, i, 0);
        } else {
            pic = h->short_ref[h->short_ref_count - 1];
            remove_short(h, pic->frame_num, 0);
        }
    }

    print_short_term(h);
    print_long_term(h);
    return (h->avctx->err_recognition & AV_EF_EXPLODE) ? err : 0;
}

int ff_h264_decode_ref_pic_marking(H264Context *h, GetBitContext *gb,
                                   int first_slice)
{
    int i, ret;
    MMCO mmco_temp[MAX_MMCO_COUNT], *mmco = first_slice ? h->mmco : mmco_temp;
    int mmco_index = 0;

    if (h->nal_unit_type == NAL_IDR_SLICE) { // FIXME fields
        skip_bits1(gb); // broken_link
        if (get_bits1(gb)) {
            mmco[0].opcode   = MMCO_LONG;
            mmco[0].long_arg = 0;
            mmco_index       = 1;
        }
    } else {
        if (get_bits1(gb)) { // adaptive_ref_pic_marking_mode_flag
            for (i = 0; i < MAX_MMCO_COUNT; i++) {
                MMCOOpcode opcode = get_ue_golomb_31(gb);

                mmco[i].opcode = opcode;
                if (opcode == MMCO_SHORT2UNUSED || opcode == MMCO_SHORT2LONG) {
                    mmco[i].short_pic_num =
                        (h->curr_pic_num - get_ue_golomb(gb) - 1) &
                            (h->max_pic_num - 1);
#if 0
                    if (mmco[i].short_pic_num >= h->short_ref_count ||
                        !h->short_ref[mmco[i].short_pic_num]) {
                        av_log(s->avctx, AV_LOG_ERROR,
                               "illegal short ref in memory management control "
                               "operation %d\n", mmco);
                        return -1;
                    }
#endif
                }
                if (opcode == MMCO_SHORT2LONG || opcode == MMCO_LONG2UNUSED ||
                    opcode == MMCO_LONG || opcode == MMCO_SET_MAX_LONG) {
                    unsigned int long_arg = get_ue_golomb_31(gb);
                    if (long_arg >= 32 ||
                        (long_arg >= 16 && !(opcode == MMCO_SET_MAX_LONG &&
                                             long_arg == 16) &&
                         !(opcode == MMCO_LONG2UNUSED && FIELD_PICTURE(h)))) {
                        av_log(h->avctx, AV_LOG_ERROR,
                               "illegal long ref in memory management control "
                               "operation %d\n", opcode);
                        return -1;
                    }
                    mmco[i].long_arg = long_arg;
                }

                if (opcode > (unsigned) MMCO_LONG) {
                    av_log(h->avctx, AV_LOG_ERROR,
                           "illegal memory management control operation %d\n",
                           opcode);
                    return -1;
                }
                if (opcode == MMCO_END)
                    break;
            }
            mmco_index = i;
        } else {
            if (first_slice) {
                ret = ff_generate_sliding_window_mmcos(h, first_slice);
                if (ret < 0 && h->avctx->err_recognition & AV_EF_EXPLODE)
                    return ret;
            }
            mmco_index = -1;
        }
    }

    if (first_slice && mmco_index != -1) {
        h->mmco_index = mmco_index;
    } else if (!first_slice && mmco_index >= 0 &&
               (mmco_index != h->mmco_index ||
                check_opcodes(h->mmco, mmco_temp, mmco_index))) {
        av_log(h->avctx, AV_LOG_ERROR,
               "Inconsistent MMCO state between slices [%d, %d]\n",
               mmco_index, h->mmco_index);
        return AVERROR_INVALIDDATA;
    }

    return 0;
}